| Directions: (Q. 1 to 5) |
| Case I: Read the passage given below and answer the following questions. |
| Anucleophilic substitution reaction that occurs by an \[{{S}_{N}}1\] mechanism proceeds in two steps. In the first step, the bond between the carbon atom and the leaving group breaks to produce a carbocation and most commonly, an anionic leaving group. |
| In the second step, the carbocation reacts with the nucleophile to form the subsitution product. The formation of a carbocation is the slow or rate determining step. |
| The rate of \[{{S}_{N}}1\] reactions decrease in the order \[3{}^\circ >2{}^\circ >1{}^\circ \], which is the reverse order observed in \[{{S}_{N}}2\] reactions. In contrast to \[{{S}_{N}}2\] reactions at sterogenic centers, which occur with inversion of configuration, an \[{{S}_{N}}1\]reaction gives a racemic mixture of enatiomers that has no optical rotation. |
| In the following questions (Q. No. 1-25), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices on the basis of the above passage. |
| Assertion: Rate of ethanolysis of \[1{}^\circ \] halide by \[{{S}_{N}}2\] mechanism is fast. |
| Reason: Carbocation is stablised by resonance. |
A) Assertion and reason both are correct statements and reason is correct explanation for assertion.
B) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
C) Assertion is correct statement but reason is wrong statement.
D) Assertion is wrong statement but reason is correct statement.
Correct Answer: C
Solution :
The ethanolysis of \[1{}^\circ \] halide generally proceeds via \[{{S}_{N}}2\] mechanism. In case if it proceeds via \[{{S}_{N}}1\] mechanism, the intermediate carbocation is unstable, since it has no adjacent carbon atom for resonance.
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